This invention relates to optical fibers, and, more particularly, to the dispensing of optical fibers from a canister within which they are wound.
Optical fibers are strands of glass fiber processed so that light beams transmitted therethrough are subject to total internal reflection. A large fraction of the incident intensity of light directed into the fiber is received at the other end of the fiber, even though the fiber may be hundreds of meters long. Optical fibers have shown great promise in communications applications, because a high density of information may be carried along the fiber and because the quality of the signal is less subject to external interferences of various types than are electrical signals carried on metallic wires. Moreover, the glass fibers are light in weight and made from a highly plentiful substance, silicon dioxide.
Glass fibers are typically fabricated by preparing a preform of glasses of two different optical indices of refraction, one inside the other, and processing the preform to a fiber. The optical fiber is coated with a polymer layer termed a buffer to protect the glass from scratching or other damage. As an example of the dimensions, in a typical configuration the diameter of the glass optical fiber is about 125 micrometers, and the diameter of the fiber plus the polymer buffer is about 250 micrometers (approximately 0.010 inches).
For such very fine fibers, the handling of the optical fiber to avoid damage that might reduce its light transmission properties becomes an important consideration. The optical fiber is typically wound onto a cylindrical or tapered bobbin with many turns adjacent to each other in a side-by-side fashion. After one layer is complete, another layer of optical fiber is wound on top of the first layer, and so on. The final assembly of the bobbin and the wound layers of optical fiber is termed a canister, and the mass of wound optical fiber is termed the fiber pack. When the optical fiber is later to be used, the optical fiber is paid out from the canister in a direction parallel to the axis of the bobbin and the canister, termed the payout axis.
It has been found by experience that, where the optical fiber is to be payed out from the canister in a rapid fashion, as for example over a hundred meters per second, the turns of optical fiber must be held in place on the canister with an adhesive. The adhesive holds each turn of optical fiber in place as adjacent turns and layers are initially wound onto the canister, and also as adjacent turns and layers are paid out. Without the use of an adhesive, payout of the optical fiber may not be uniform and regular, leading to snarls or snags of the fibers that damage them or cause them to break as they are payed out. On the other hand, the use of an adhesive requires attention to the "lift off" of each turn of optical fiber from the fiber pack, to ensure smooth payout.
In one application, an optical fiber is used to transmit sensor signals from, and guidance commands to, a moving vehicle from a stationary or moving controller. The canister is mounted in the rear of the vehicle, and the optical fiber payed out from the canister as the vehicle moves. The optical fiber must be payed out in a uniform manner without undue stress, to avoid breakage or kinking of the optical fiber.
In the past there has been some difficulty in achieving an acceptable payout of the optical fiber, particularly where both the vehicle carrying the canister and the controller are moving and turning during the payout process. Ensuring lift off of the optical fiber from the fiber pack and minimizing frictional effects have been of particular concern. There is therefore a need for an improved approach to optical fiber payout from a canister. The present invention fulfills this need, and further provides related advantages.